a noun clause serving as the object of the preposition.
我覺得可能是
所有跟帖:
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                    謝謝rancho的答疑,現在明白多了。Have a nice new week!
                     -beautifulwind- 
                    ♀                    
                        
                    
                                                            
                        
                    
                                        
                    
                    
                                        
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                        09/13/2015 postreply
                                                18:41:28